Novak Djokovic is put through some stretching exercises on the eve of his Wimbledon final against Andy Murray. Photograph: Jonathan Brady/PA

After Andy Murray's semi-final victory against Jerzy Janowicz on Friday night he was asked about the man now standing in his way in Sunday's Wimbledon final. What was his friendship with Novak Djokovic like these days? How did it compare with their friendship as juniors? Was it, in fact, even a friendship any more? That Murray should seem briefly lost for an easy answer seems doubly significant given that moments later he had little problem coming up with a response to what he might expect the ghost of Fred Perry to say to him should the deceased former champion stage a visitation before the final (answer: "Why aren't you wearing my kit?").

In the end Murray settled on a slightly awkward definition. "We have a professional friendship," the British No1 said of a man born a week before him, whose progress has entwined itself around his own with fraternal claustrophobia from their shared attendance at junior training camps and since then along a 14-year professional path that sees them currently ranked No1 and No2 in the world and all set to inflict further mutual agony across the fraught and peculiarly personal sporting collision that is a grand slam final.

Asked the same question on the eve of Sunday's final Djokovic was, characteristically, a little more forthcoming. "Yeah, we know each other since we were 11 years old. Always very fair, very honest relationship. You know, now we are big rivals and it's difficult. So we don't get together and have dinners and parties, but we definitely always chat and remember the fun days we had as juniors."

Seventeen years on from their first meeting on court as boys ("All I remember is his curly hair") Djokovic and Murray have eight shared tour finals, with the Serb ahead 2-1 in the grand slam events and Murray the victor in their one meeting on grass, the Olympic semi-final on Centre Court last year. Beyond the bald outline of their conjoined career arcs – and Djokovic, with six grand slam titles to Murray's one has won that battle outright so far – it is the contrast between the two that seems particularly illuminating.

Like Murray's, Djokovic's career can be divided into two distinct sections: an early plateauing out, accompanied by a sense of a certain callowness to be overcome; followed by an abrupt ignition into Djokovic 2.0, the steep mid-career ascent towards hall-of-famer status and his current incarnation as three-year world No1 and an athlete of almost preternatural mental resilience and physical bravura of flexibility and endurance.

As for Murray, the transition for Djokovic seems to have involved a process of extreme and transformative physical conditioning, of coming to terms in some basic sense with his own body. Certainly it seems scarcely credible now that, as recently as the summer of 2010, Djokovic had a reputation as a quitter, a strop artist and something of a pussycat. The same Djokovic, whose teak-framed match-hardness is one of his most revered qualities before a Wimbledon final that seems likely to unfurl into a savage test of stamina, walked off court seven times in his early career, citing among other things a blister and straightforward fatigue. It now seems likely Djokovic, who is nautically slight among the slabbed and beef-caked specimens of the men's tour, was simply growing into his physique, finding a way to deploy his greater speed and that thrillingly gymnastic flexibility. A gluten-free diet is credited with sculpting out his current middleweight boxer's physique, and the superior power-to-weight ratio that allows him to glide about like a pond-skater, intimidatingly quick across the ground and a relentlessly high-pressure presence on court.

Beyond this the real turning point for Djokovic seems to have come with his starring role in Serbia's Davis Cup victory in the Belgrade Arena in 2010, an extraordinarily stirring occasion in the recent history of this infant nation and the pistol shot that set him off on that famous 43-match unbeaten run. Djokovic had one of the great sporting years in 2011, winning 10 tournaments, including Wimbledon and the Australian and US Opens and gathering a record $12m in prize money.

It is perhaps a little too tempting to lump together that yeastily seductive nexus of emergent Serbian nationalism and Djokovic's own bloom into the dominant tennis player in the world. And it is as much family as nationality that seems to define his early life. His father was a downhill skier and young Novak famously grew up on Mount Kopaonik, where his parents ran a fast-food joint: spotted at four by his mentor Jelena Gencic – who died in June – the 12-year-old Nole was packed off to the Pilic tennis academy in Oberschleissheim, Germany.

Home, though, has always remained a potent presence for a man who remains not just Serbia's only grand slam winner, or indeed tennis player of any note, but his country's most visible citizen full stop. After that 2011 Wimbledon victory Djokovic was greeted in Belgrade by a 100,000-strong party in the city's main square ("The most beautiful experience I had as a person, as an athlete," he says now) and he remains an object of slightly capricious Serbian pride, celebrated for his victories, mildly castigated in defeat.

Not that there are many of those these days. Djokovic remains a player who is simply good at everything, with an all-round game without weaknesses, and that uniquely gymnastic physique to make up the slack where he might lack the brute physicality of some opponents. Just as bulked up all-round power and almost alarming levels of endurance have become Murray's secret weapon, so extreme flexibility, captured in eye-watering detail by Wimbledon's slow-motion cameras, has become Djokovic's most notable superpower. And as Murray obsessively monitors his physical intake, so Djokovic begins each day with an eye‑watering hamstring stretch, and then stretches at every free moment.

Like Murray, with whom he remains good friends for all the slight wariness – in 2011 the Serb visited Murray's home town on holiday and rather endearingly texted him a picture of a Dunblane road sign – Djokovic remains an oddly obsessive, strangely compelling 26-year-old champion tennis player. For now he holds the centre ground in their shared journey through elite tennis: the professional friend who knows Murray perhaps as well as it is possible to in these terms, and who will stand in his way again on the biggest occasion of Murray's own sporting life on Sunday.

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